Fluidized powder flow and control



July 10, 1951 E. LIEDHOLM 2,560,356

FIJUIDIZED PQWDER FLOW AND CONTROL Filed July 1, 1947 2 Sheets-Sheet l Producl' Oil Vapoq g 1 Skarn L lnvzn'hzr: Gzorqz E. Licdholm b g his Ai+ornzg: g%i% y- 1951 e. E--LIEDHOLM 2,560,355

FLUIDIZQD POWDER FLOW v w: CONTROL Filed-July 1, 1947 2 Sh eets-Sheet 2 lnvenior: George E..Ljedh'olm 59 his A++omz z% Patented July 10, 1951 FLUIDIZED POWDER FLOW AND CONTROL George E. Liedholm, Berkeley, Calif., assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application July 1, 1947, Serial No. 758,446

9 Claims.

This invention relates to a new and improved method for contacting two separate gaseous fluids with a fluidized powder which is recirculated through two separate zones at a controlled rate. More particularly the invention relates to a method for accomplishing the above while controlling the flow without the use of mechanical valves in the stream of said recirculated powder.

In many processes it is desirable to contact two or more gaseous fluids separately with a solid material which may be a catalyst, a refining agent, a heat carrier material, or may be the material acted upon or treated. Examples of a few types of processes of this kind are the treatment of hydrocarbon oils, the oxidation of naphthalene, the reduction of ores, the gasification of coals, the retorting of shale oil, and the recovery of vapors from gases by absorption. In most of such cases various important and recognized advantages can be gained by employing the solid material as a powder in the so-called fluidized or pseudo liquid state. Most non-sticky solids when brought to a suitable state of subdivision, for example passing a thirty-mesh sieve or finer,

can be brought to the so-called fluidized or pseudo liquid state by limited and controlled aeration with any gas or vapor. For further par-' ticulars regarding the fluidized or pseudo liquid state reference may be had to the Petroleum Refiner 25 No. 9,435,442 (September 1946) and U. S. Patent No. 2,357,901. One of the chief advantages gained by employing the solid material in a pseudo liquid state is that since it behaves very much like a true liquid it can be easily transported from one vessel to another. In most applications of the so-called fluidized technique the powder is caused to flow by the use of a carrier gas, which is normally one of the gaseous reactants or products of the process. Such systems have come into limited application in a number of fields; however,they have been particularly developed in the field of catalytic treatment of hydrocarbon oils. In the systems hitherto used the flow of powder in the process has been regulated and controlledby the use of one or more mechanical valves in the stream of fluidized powder. Various types of valve arrangements have been tried and suggested, including screw feeders, star feeders, lock chambers and the like. However, the most satisfactory and the most widely used arrangement is a hydraulically operated slide valve. This arrangement, although the best so far found, is far from satisfactory. In practice the slide valves, even though heavily constructed of wear-resistant material, are quickly eroded by the powder to the extent that they do not function properly. In view of this it is the standard practice to provide two slide valves instead of one so that when the first ceases to function properly the second can be brought into use without stopping the run. Furthermore, the present known flow control valves are not suited for use at temperatures above about 1200 F.

In cases where the powder is fed into a pneumatic-conveying system by means of a mechanical device controlling the flow (such as a slide valve, mechanical feeder, or the equivalent) and the powder is picked up by a stream of gas, the powder is dispersed in the gas and conveyed primarily by the force of the gas flow. In most cases the powder is transported twice by such means in completing its cycle although several systems have been suggested in which the powder is conveyed by a gas stream only once. The object of the present invention is to provide a method in which the flow of the powder may be controlled without resort to the use of slide valves or equivalent mechanical device in the stream of powder. Another object of the invention is to provide a method of operation which is particularly advantageous for use when temperatures above about 1200 F. and including 2000 F. are encountered in the circulating powder. It is particularly in this range where control of the flow by mechanical means is most diflicult. Other objects of the invention are to provide methods for the control of the flow in accordance with changes of suitable indicia within the system.

The process of the invention is a process for contacting two gaseous fluids, A and B, in separate contact zones, an upper zone I and a lower zone 2, with a fluidized powder which is continuously recycled through said zones. It comprises the steps of passing fluid B through lower zone 2 countercurrent to the flow of powder therethrough at a substantially constant rate sufficient to maintain the powder in said zone in a pseudo liquid state, maintaining a positive superatmospheric pressure of said fluid B above the pseudo liquid powder in said zone, allowing pseudo liquid powder from said zone to ,pass unhindered and continuously by the force of gravity and said positive pressure into a transfer zone of restricted cross section compared to said lower zone 2, said transfer zone communicating with the bottoms of the upper and lower zones l and 2, maintaining a bed of said powder in pseudo liquid state in upper zone I above said lower zone 2, dividin the gaseous fluid A into two portions, passing'the first 0f said portions into the said powder in said transfer zone, passing the second of said portions of gaseous fluid A directly into said bed of powder in said upper zone I, continuously allowing powder in pseudo liquid state to pass unhindered and continuously by gravity from upper zone I to lower zone 2, adjusting and controlling the pressure of said fluid A and/or B above the pseudo liquid powder in upper zone I and/or lower zone 2 (i. e. the differential pressure between said fluids) and controlling the rate of circulation of said powder through upper zone I and lower zone 2 and said transfer zones by the control of the ratio of said two portions of said fluid A, whereby the circulation of said powder is caused by a lessened static head of pseudo liquid powder in said transfer zone due to the controlled aeration of the pseudo liquid powder therein by the controlled portion of said fluid A.

The method of the invention is applicable in any of the various processes where it is desired to contact two separate gaseous fluids with a solid material in powder form. However, for the purpose of explaining the method of operation, the invention will be described as applied to a process for the production of gasoline from high-boiling hydrocarbon oils. To aid in this description, reference is had to the attached drawings, Figures I and II. Figure I illustrates semi-diagrammatically a side view, partly in section, of one suitable apparatus. Figure II is a horizontal section taken through IIII showing the arrangement of the cooling coils and header. Only the pertinent parts of the apparatus are illustrated. In the interest of clarity the various auxiliary apparatus and reflnements common in catalytic cracking systems have been omitted. Some of these secondary matters will be mentioned in the description; however, it is to be understood that the method of the invention is not to be limited by the reference or lack of reference to any such secondary features which are considered to be well known in the art.

Referring to the drawing, Figure I, the oil to be cracked, preferably in vapor form, is introduced at a controlled and substantially constant rate via line I. The oil passes via a distributing ring 2 and a series of injection nozzles 3 into the lower zone, which in this case is the cracking zone. The cracking zone is fllled up to a controlled level, indicated approximately by the shading, with a suitable powdered cracking catalyst which is maintained in a fluidized (pseudo liquid) state. The process is not limited to the use of any particular catalyst. Merely by way of example, suitable catalysts are the conventional synthetic silica-alumina cracking catalysts and the treated clay cracking catalysts now in commercial use. The catalyst may be ground to pass a IOU-mesh sieve or it may be one of the so-called microspheroidal catalysts in which the particles are tiny balls of about 20 to 1000 microns in diameter. The density of the fluidized catalyst bed is maintained at a suitable desired level, forexample 30 pounds per cubic foot. This is controlled in the normal manner by controlling the rate of the injection of the oil feed. Hot freshly regenerated catalyst continuously enters the reaction zone via line 4. Line 4 is of relatively large diameter and unrestricted by mechanical flow-controlling devices; however, it is of relatively small cross section as compared to the reaction zone. Line 4 is of sufficient length that its lower end dips below the level of the fluidized catalyst in the reaction zone thereby creating a liquid seal. A small amount of any suitable aeration gas may be introduced near the bottom of line 4 via line 5 to maintain the catalyst therein in a freely flowing pseudo liquid state. The oil vapors, after passing ,up through the lower reaction zone and being cracked therein, are withdrawn via line 6. Any entrained catalyst is separated by the centrifugal separator 'I and returned to the reaction zone via line 8. The cracked vapors then are removed via line II containing valve III. The cracking zone may be advantageously restricted somewhat in cross section near its lower end, and an inert gas, such as steam, may be introduced near the bottom via line I2 to reduce the concentration of volatile hydrocarbons passing out of the reaction zone with the partially spent catalyst. The partially spent catalyst withdrawn from the reaction zone flows by gravity into transfer line I3. Transfer line I3 defines the transfer zone mentioned above. This line is unobstructed by valves or mechanical feeding devices; however, an emergency valve may be provided if desired. Such a valve would normally be maintained in a wide open position where it would not offer any restriction and would not be subject to erosion. It would be provided, if at all, only to prevent a blow-back in case of an emergency and, therefore, has not been indicated in the drawing. Line I3 must define a substantially unobstructed zone of sufficient diameter to allow a substantial flow of catalyst in the pseudo liquid state under the influence of a small pressure head. This line should not have sharp bends or any substantial horizontal runs.

The partially spent catalyst from the lower (reaction) zone is passed via line I3 into the lower part of the upper (regeneration) zone wherein it is regenerated by burning off carbonaceous deposits with air or oxygen or other regeneration mediums introduced via lines I4 and 24. The catalyst in the upper (regeneration) zone is maintained in a pseudo liquid state and at a level (dependent upon the level in the lower reaction zone, the degree of the aeration, the amount of carbon in the catalyst, and upon the amount of the catalyst charged to the system) somewhat as indicated by the shading. The regeneration is quite exothermic. In order to avoid damaging the catalyst by overheating, cooling coils I5 are provided. These coils connect to manifold lines I6 and II, which, in turn, connect to a suitable boiler I8.

The spent regeneration gas (flue gas) is withdrawn at the top via line I9. Any entrained catalyst is collected in a centrifugal separator 20 and returned to the regeneration zone via line 22. The catalyst-free gas passes out via line 2| containing valve 9.

The air or oxygen supplied to regenerate the catalyst is split into two portions at valve 23. The main portion is passed directly to the regeneration zone via line I4. The other portion is passed via line 2 into the transfer line I3. It is preferably introduced on the outside of the bend, as illustrated, to decrease the possibility of blowing back into the reactor. Very minor amounts of any suitable fluidizin'g gas may be introduced at the bottom of the bend via lines 25 and 26 to prevent plugging at this point.

The catalytic cracking and regeneration of the catalyst may be carried out under the usual applicable range of conditions of temperature, pressure and contact time in accordance with the particular catalyst used, the particular oil cracked,

asc acc and the particular product desired. Merely by way of example, theh following conditionsmay be employed in the reaction zone:

Temperature F 975 Pressure p.s.i. g. 12 Liquid hourly space velocity 0.75 Catalyst/oil, weight ratio 7:1 Bed density "pounds per cubic foot 31 Catalyst bed height feet 15 In the above the apparatus and the various flows have been described in connection with a catalytic cracking operation. Characteristic features of the apparatus and flow are: (1) one zone is above the other; (2) the zones directly communicate in such a manner that their static heads are additive, i. e. the catalyst can flow directly without passing over a weir; (3) the flow of catalyst is not controlled at any point in the circuit by a valve, a star feeder or any equivalent mechanical device; i) if the amount of catalyst in the system is considered to be constant, the amount of catalyst in either zone may vary over wide limits, and the amount of catalyst in the other zone will vary an equal amount in the opposite direction, 1. e. the amount of catalyst in :both zones may be equal, or the catalyst may be distributed between the two zones in any proportion over a wide range.

In the system described the flow of catalyst :from the lower zone to the upper zone via transfer zone I3 is not caused by, or appreciably affected by, the carrying power of the gas introduced via line 24, but is affected by gravity flow caused by a difference in head on the two sides of the lower bend in line It. This difference in head is controlled by maintaining a desired minor difference in density in the pseudo liquid powder in the lower contact zone and the transfer zone 53. The density of the pseudo liquid. powder in the lower zone is dependent upon several variables, including the pressure thereon. The density of the pseudo liquid catalyst in the transfer line I3 is dependent primarily upon the amount of aeration gas supplied thereto. The total amount of gas supplied to the upper zone by the two respective paths may be retained substantially constant.

Having described the apparatus and the flows, consideration will now be given to the method of control. It will be seen that the known meth- Od of control, commonly employed in systems containing one or more slide valves, mechanical feeders, or other equivalent devices, are not applicable in the present system. In systems wherein one or more valves or the equivalent is used the various variables may be independently fixed and controlled. In the described system, on the other hand, the various variables are interdependent and are simultaneously controlled with respect to each other.

The following are the more important variables, control of which is desirable in order to efficiently carry out, various processes:

1. Contact time of the reactant vapor with the powder in the reaction zone.

2. Residence time of the powder in the reaction zone.

3. Temperature in the reaction zone.

4. Pressure in the reaction zone.

The contact time of the reactant with the powder in the reaction zone is not only dependent upon the rate of feed of the reactant, but is also dependent upon the height of the bed in the reaction zone and the'degree of conversion (which latter, in turn, is a function of the catalyst activity, residence time of the catalyst, temperature, 'etc.). The residence time of the pow der in the reaction zone depends upon the height of the bed in the reaction zone and upon the rate of'circulation (which, in turn,is affected by the several variables). The temperature is depend= ent upon the rate of circulation of the powder and the degree of conversion (due to the heat of reaction). The pressure may be independently controlled with sufficient precision over a wide range. Thus the entire system may be operated under any pressure from somewhat below atmospheric pressure up to several hundred atmospheres. While the height of the bed in the reaction zone and the rate of circulation of the powder are dependent upon and controlled by pressure differences, these are only affected to a minor extent by the gross pressure on the system.

The mentioned important variables may be controlled by control of one or more of the variables affecting them. However, since in the described system there is no unique variable by which the mentioned important reaction variables (except total pressure) may be controlled, it is necessary to control two or more variables simultaneously and with respect to eachother. It is found that this can be done in more than one way. In the interest of clarity the controls will be separately described before describing their interdependence. It will be understood, therefore, that no one of these described controls is to be'considered as controlling per se any single reaction variable. To aid in the description of the controls reference is had to the attached drawings, Figures III, 111a, I111), I110, IIId, IV, V, VI, and VII.

Figure III illustrates diagrammatically one control which will hereinafter be referred to as control III. In" this control the pressure above the pseudo liquid bed in the lower zone is made responsive to changes in height of the pseudo liquid bed. This control affects the height of the pseudo liquid bed, the pressure, and the circulation rate, and, consequently, affects all of the important process variables to a greater or less extent. known control elements affording control of the pressure above the pseudo liquid bed in accordance with the changes in the height of the pseudo liquid bed may be used, a preferred means of accomplishing this is by means of a differential pressure controller. This is illustrated diagrammatically in Figure III. Referring to Figure III, the pressures at a point near the bottom of the pseudo liquid bed and at a point above the pseudo liquid bed are conveyed through lines EDI and 362, respectively, to a differential pressure controller (DPC) 383 arranged in the known manner to control the setting of valve It in accordance with the changes in the differential pressure. All of the parts of the system are conventional and the various ways of combining them to obtain the desired control will be apparent to those skilled in this art. The operation of valve It] in accordance with the changes in the differential pressure may be effected with a servo motor or other suitable known equivalent device operated by electricity, magnetism, air pressure, liquid pressure, steam, or the like. In Figure III the controller and the valve actuator are indicated diagrammatically as being connected through wirin 304.

In Figure III that portion of the control illustrated and discussed operates as follows. Any

While any mechanical arrangement of change in the height or density or botlifif the lower fluidized bed affects the differential pressure and therefore the diifere'ntial pressure controller 303. This controller is arranged in the known manner to increase the opening in valve when the differential pressure falls below the desired value (and vice versa). Since'the setting of the valve in line 2| is in'this caseiunchanged this causes the flow from the upper zone to the lower zone to increase until the differential pressure exceeds the d'esiredvaluefat which time valve II] is throttled. Thus, the opening of valve It causes the level in the'lowe'r bed to be raised to the desired value through altering the rates of flow and also throughexpansion of the lower bed caused by the decreased pressure. This of itself, however, does noticestablish thedesired condition since'fthe opening of valve it also decreases the fiow"throughthe rising leg (I3 in Fig. I).

The control illustrated in FigureIIIa, hereinafter referred to as control IIIa, i similar: in an respects to that of the described control III-except that the pressure above the upper, instead of the lower, pseudo liquid bed is controlled through control of valve 9, and the polarity is reversed, i. e. in control III valve [0 is'moved to a more open position with decrease of the differential pressure, and in control IIIa valve 9 is moved to a more closed position with 'decrease of the differential pressure.

Since the level of the pseudo liquid bed in'the upper zone depends upon the level ofthe pseudo liquid bed in the lower zone, two further variations of control III can be used. Thus, in controls III?) and IIIc, illustrated diagrammatically in Figures 1111) and 1110, the differential pressure between a point near the bottom of the upper pseudo liquid bed and a pointabove the level of the pseudo liquid bed is used to effect control of the valves I0 and 9, respectively.

Thus that portion of the control illustrated in Figure 1112) operates as follows. Any change in the height or the density or both of the lower bed is reflected in the height of the upper bed and hence in the differential pressurein the differential pressure controller. In this case the controller is arranged to throttle valve I!) when the differential pressure falls below the desired value. I trol illustrated in Figure 1110 is to that of Figure IIIbas'that of Figure 11111 is to that of Fig-- ure III; that the differential pressure between points above and within the upper fluidized bed is used to control the back pressure above the bed. This back pressure also affects the pressure above the lower bed to an'almost equal extent. The differential pressure'controller is arranged to throttle valve 9 when'the differential pressure increases above the desired value for the particular operation. 7

One further modification of control III hereinafter referred to a control IIId is suitable in the present system. In this modification, illustrated diagrammatically in Figur IIId, the pressure differential used to regulate valve I0 is between the vapor space above the pseudo liquid bed in the lower zone and a point near the bottom of the pseudo liquid bed in the'upper zone.

The differential pressure in this case varies with the conditions similar to'the changes in the differential pressure effective in thecases illus-' trated in Figures III-IIIc. Ittherefore may be used to control-the pressure above the-' bsds in The variations of this part of the conthe same manner. In the case illustrated the differential pressure controller is arranged to increase the opening in valve [0 when the differential pressure exceeds the desired value.

The above described control III and its modifications affect the pressure above the pseudo liquid bed in the lower zone or the upper zone and thereby the various other variables,-as explained above. These controls, either aloneor with various combinations with one another, are not capable per se of affording the desired control of the described system in which valves are not used to control the circulation rate; a second control is necessary.

According to the present invention, the second control is-afforded by control of the ratioor-proportion of gas passed by the two respective paths described, 1. e. by control of valve 23. Thus. with the opening of valve 9 or the throttling of valve [0, or both, valve 23 is readjusted to decrease the proportion of gas via line 24. Valve 23 can be manually controlled; however, an automatic control in accordance with suitable indicia is preferred.

One such control is illustrated diagrammatically in Figure IV. In this control system valve 23, after being set manually, is controlled automatically by a conventional differential pressure controller 40! connected by line 402 and 403 to lines '2l and II, respectively. In the case illustrated the diiferential pressure controller'is arranged to decrease the proportion of gas passed via line 24 and to thereby increase the proportion of gas passed via line M as the differential pressure between lines 2| and Ii increases above the desired value, and to reverse the change as the differential pressure falls below the desired value. As previously explained, as the differential pressure between lines 2| and II is decreased due either to the opening of valve I0 or the throttling of valve 9 this not only affects the level of the beds but also decreases the rate of flow in the rising leg (I3 in Figure I). This upset is counteracted by the adjustment ofthe valve 23 as indicated. Since, as "a rule, the pressure in either line 2| or H is held substantially constant, the control is, in effect, determined by whichever of these pressures is allowed orcaused to vary. In most cases, there fore, a simple pressure controller rather than a differential pressure controller responsive to the pressure in either line 2| or H may be used to control valve 23. These variations may bedesignated controls Wu and Nb, respectively (not illustrated) Since in the control systemIII described above the pressure in lines ll and/or 2| is controlled through a differential pressure controller sen-- sitive to'pressure changes between points above and below the normal level of thepseudo-liquid powderin either zone, it is also possible-to control valve 23=in response to a differential pressure controller such as differential pressure'con troll'er 303 of Figure III. This method of control is illustrated diagrammatically in Figure V. The differential pressure controller in Figure V corresponds to the differential pressure controller 303 in Figure III and has been designated by this reference number. In the case illustrated the differential pressure controller is arranged to decrease the proportion of gas passed via line 24-by adjustment of valve'23 as the differential pressure increases above the desired value. The differential pressure controller can also, if desired. be located --as illustrated in Figure III b or Figure 'IIId, instead of as in Figure III and .Figure V. These variations of the control illustrated in Figure V may be called controls Vb and Val, respectively (not illustrated). In case ""Vb the differential pressure control is arranged to adjust valve 23 to decrease the proportion "of gas passed via line 24 as the diflerential pres- "sure decreases. In case Vol the differential pressure controller is arranged to adjust valve 23 to temperature in the reaction zone (in this case .the lower zone) below the level of the fluidized bed are caused to actuate a temperature controller (TC) 602. In practice, the temperature sensitive device is suitably a thermocouple connected through wiring 60!, but other known temperature sensitive instruments may be substituted. The temperature controller, which is a conventional piece of control equipment, is then connected to the valve motor or other valve actuatin device by electrical connection 603. After manual setting of valve 23, this valve is controlled in accordance with changes in temperature in the fluidized bed of powder in the lower zone. Thus in the case illustrated the temperature controller 602 is arranged to throttle valve .23 as to line 24 as the temperature increases, and vice versa.

The controls illustrated in Figures IV, V and VI are controls that may be used in conjunction with control III to provide the desired control of the process variables in the described system. Thus, any of the variants of control III (i. e. controls III and Illa through 11112) may be combined with any of controls IV, IVa, IVb, V, Vb, Vd or VI. While this aifords a number of combinations these are minor variations of one basic control system having two branches. This basic control is (1) control of the gas pressure of one of the effluent gases in accordance with the differential pressure changes between I an efliuent gas and a point below the normal level of the fluid powder, and (2) control of the proportion of gas passed to the upper zone via the two paths in accordance with said first control to maintain a proper controlled system at any desired set of condtions within the limits of the design of the plant. The sub-branches are (1) that in which the second of the above mentioned controls is made responsive to pressure changes within the system, and (2) that in which this control is made responsive to temperature change within the system. As pointed out, the second basic control can, at least theoretically, be carried out manually, but is preferably carried out automatically by one of the systems illustrated in Figures IV, V or VI or their mentioned variants. An example of such a combined control system is illustrated in Figure 1 of the drawing. In the control system illustrated diagrammatically in this figure, control III (illustrated in Figure III) is combined With control V (illustrated in Figure V). In this system any change in the flow rate caused by change in the amount of carbon in the powder,

amount of reaction taking place, or any other.

of the various possible factors influencing the flow rate, cause a change in the level of fluidizedpowder in both the upper and'lower zones. This change affects the difierential pressure controller, which, in turn, automatically adjusts valve 23 to reestablish the chosen circulation rate and simultaneously adjusts valve [U to reestablish the remaining interdependent conditions mentioned above. On the other hand, when the level of the fluidized powder in the lower zone changes due to any one of the several factors influencing it, such change in the bed level causes the differential pressure controller 303 to adjust valve [0 to reestablish the chosen bed height. In making this adjustment, however, the pressure in line 6 is changed and this change is reflected in the circulation rate. In the described system, however, this latter change is compensated for by simultaneous control valve of 23.

An example of the other main type of combination control is illustrated diagrammatically in Figure VII. Any changes in the flow rate are immediately reflected in the temperature in the fluidized bed in the lower zone. As the temperature drops, the temperature controller 602 causes valve 23 to be moved to divert more of the gas via line 24; this, however, causes the bed level to change (drop). This undesiredchange is compensated for by readjustment of valve l0 (slight opening). This latter adjustment has a secondary influence on the flow rate which is, in turn, compensated for until the desired equilibrium conditions are reestablished. Except when a condition is purposely altered manually by resetting a control, no appreciable variation in the set conditions is allowed to take place, since minor changes are immediately corrected. While the temperature is preferably taken in the pseudo liquid powder in the reaction zone the temperature may also, if desired, be taken at any other convenient point in the pathof the recirculated powder.

In the above the apparatus, flows and controls have been described in connection with a cracking operation in which the cracking takes place in the lower zone and the catalyst is regenerated in the upper zone. In this case the oil vapor enters via lines I and the material entering via lines l4 and 24 is regeneration as (air). It will be understood that the operation may be turned around and that in many cases this will be more desirable. In such cases the lower zone may be the regeneration zone and the reaction may be carried out in the upper zone.v In such cases the reactant is split into two portions which are introduced into the reaction zone via lines l4 and 24, respectively.

' I claim as my invention:

1. In a process for contacting two gaseous fluids A and B in separate contact zones I and 2 zone I being above zone 2 with a fluidized powder which is continuously recycled through said zones, the combination of steps comprising passing fluid B through lower zone 2 countercurrent to the flow of powder therethrough at a substantially constant rate suflicient to maintain the powder in said zone in a pseudo liquid state, maintaining a positive superatmospheric pressureof said fluid B above the pseudo liquid powder in said zone, allowing pseudo liquid powder from the lower zone 2 to pass unhindered and continuously by the force of gravity and said positive pressure into a transfer zone, said transfer zone communicating with the bottoms of the upper and lower zones I and 2 and being ;of restricted cross section compared to said lower zone 2, maintaining a bed of. said powder in pseudo liquid state in upper zone I abovesaid lower zone 2, dividing the gaseous fluid A into two portions passing the first of said portions intothe said powder in said transfer zone passing the second of said portions of gaseous fluid A directly into said bed of powder into upper zone I continuously, allowing powder in pseudo liquid state to pass unhindered and continuously by gravity from upper zone I to lower zone 2,,and controlling the conditions and circulation rate-of said powder by controlling the ratio of said two portions of said fluid A and the pressure difierences between points above the pseudoliquid powder in said two zones in response to variations in the differential pressure measured between a point in a fluidized bed in one of the zones and a point above a fluidized bed in one of the zones.

2. In a process for contacting two gaseous fluids .A and B in separate contact zones 1 and 2. zone I being above zone 2 with a fluidized powder which is continuously recycled through said zones, the combination of steps comprising passing fluid B through lower zone-2 countercurrent to the flow of powder therethrough at a substantially constant rate sufiicient to maintain the powder in said zone in a pseudo liquid state, maintainin a positive superatmospheric pressure of said fluid'B. above the pseudo liquid powder in said zone, allowing pseudo liquid powder from lower zone 2 to pass unhindered and continuously by the force of gravity and said positive pressure into a transfer zone, said transfer zone communicating with the bottoms of the. upper and lower zones I and 2 and being ofrestricted. cross section compared to said lower zone 2,, maintaining a bed of said powder in pseudo liquid state. in upper zone I above said lower zone 2, dividing the gaseous fluid A into two portions, passing the first of said portions into the. said powder in said transfer zone passing the second of said portions of gaseous fluid A directly into said bed of powder into upper zone I continuously, allowing powder in pseudo liquid state to pass unhindered and continuously by gravity from upper .zone I to. lower zone-2 and controlling the conditions and circulation rate of said powder by control of the pressure difference between points abovev the pseudo liquid powder in said two zones and control of the ratio of said two portions of said fluid A, said control of the pressure difference between pointsabove pseudo liquid powder in said two zones being effected in response to changes in difi'erential pressure between a, point above and a point below the level of the pseudo liquid powder in one of said zones.

3. In a process for contacting, two gaseous fluids A and B in separate contact zones I and 2 zone I being above zone 2 with a fluidized powder which is continuously recycled through said zones, the combination of steps comprising passing fluid B through lower zone 2 countercurrent to the flow of powder therethrough at a substantially constant rate sufficient to maintain the powder in said zone in a pseudo liquid state, maintaining a positive superatmospheric pressure of said fluid B above the pseudo liquid powder in said zone, allowing pseudo liquid powder from lower zone 2 to pass unhindered and continuously by the force of gravity and said positive pressure into a transfer zone, said transfer zone communicating with the bottoms of the upper and lower zones I and 2 and being of restricted cross section compared to said lower zone 2, maintainin a bed of said powder rate of said powder by control of the pressure difference between points above the pseudo liquid powder in said two zones and control of .the ratio of said two portions of said fluid A, said control of the ratio of said two portions of said fluid Avbeing efiectedin response to changes in differential pressure between a point above and a point below the level of the pseudo liquid powder in one .of said zones.

4. In a process for contacting two gaseous fluidsA and Bin separate contact zones I and .2 zone I being above zone 2 with a fluidized powder which is continuously recycled through said zones, the. combination of steps comprising passing fluid. B through lower zone 2 countercurrent no the flow of powder therethrough at a substantially constant rate sufficient to maintain the powderin said zone in pseudo liquid state, maintaining a positive superatmospheric pressure of said fluid B above the pseudo liquid powder in said ozone, allowing pseudo liquid powder from lower zone 2 to pass unhindered and continuously by the force of gravity and said positive pressure into a transfer zone, said transfer zone communicating with the bottoms of the upper and lower zones. I and 2 and being of restricted cross section compared to said lower zone 2, maintaining. a bed of said powder in pseudo liquid state in upper zone I abovesaid lower zone 2, dividing the gaseous fluid A into two portions, passing the first of said portions into the said powder in said transfer zone passing the second of said portions of gaseous fluid A directly into said bed of powder into upper zone I continuously, allowingpowder in pseudo liquid state topass unhindered and continuously by gravity from upper zone I to lower zone 2 and controlling the conditions and circulation rate of said powder by control of the pressure difierence between points above the pseudo liquid powder in said two zones and control of the ratio of said two portions of said fluid A, said controls being effected in response to changes in differential pressure betweena point above and a point below the level of the pseudo liquid powder in one of said zones.

5. In a process for contacting two gaseous fluids A and B in separate contact zones I and 2 zone I being above zone 2 with a fluidized powder which is continuously recycled through said zones, the combination of steps comprising pass.- ing fluid B through lower zone 2 countercurrent to the flow of powder therethrough at a substantially constant rate suflicient to maintain the: powder in said zone in a pseudo liquid state, maintaining a positive superatmospheric pressure of said fluid 3 above the pseudo liquid pow der in said zone, allowing pseudo liquid powder from lower zone 2 to pass unhindered and continuously by the force of gravity and said positive. pressure into a transfer zone. said transfer zone communicating with the bottoms of the upper and lower zones I and 2 and being of. restricted cross section compared to said lower.

13 7 zone 2, maintaining a bed of said powder in pseudo liquid state in upper zone I above said lower zone 2, dividing the gaseous fluid A into two portions, passing the first of said portions into the said powder in said transfer zone passing the second of said portions of gaseous fluid A directly into said bed of powder into upper zone I continuously, allowing powder in pseudo liquid state to pass unhindered and continuously by gravity from upper zone I to lower zone 2 and controlling the conditions and circulation rate of said powder by control of the pressure vdiiference between points above the pseudo liquid powder in said two zones and control of the ratio of said two portions of said fluid A, said control of the ratio of said two portions of said fluid A being eflected in response to changes in temperature of the circulated pseudo liquid powder.

6. In a process for contacting two gaseous fluids A and B in separate contact zones I and 2 zone I being above zone 2 with a fluidized powder which is continuously recycled through said zones, the combination of steps comprising passing fluid B through lower zone 2 countercurrent to the flow of powder therethrough at a substantially constant rate suflicient to maintain the powder in said zone in a pseudo liquid state, maintaining a positive superatmospheric pressure of said fluid B above the pseudo lquid powder in said zone, allowing pseudo liquid powder from lower zone 2 to pass unhindered and continuously by the force of gravity and said positive pressure into a transfer zone, said transfer zone communicating with the bottoms of the upper and lower zones I and2 and being of restricted cross section compared to said lower zone 2, maintaining a bed of said powder in pseudo liquid state in upper zone I above said lower zone 2, dividing the gaseous fluid A into two portions, passing the first of said portions into the said powder in said transfer zone passing the second of said portions of gaseous fluid A directly into said bed of powder into upper zone 5, continuously allowing powder in pseudo liquid state to pass unhindered and continuously by gravity from upper zone I to lower zone 2 and controlling the conditions and circulation rate of said powder by control of the pressure difference between points above the pseudo liquid powder in said two zones and control of the ratio of said two portions of said fluid A, said control of the pressure diflerence between points above pseudo liquid powder in said two zones being effected in response to changes in differential pressure between a point above and a point below the level of the pseudo liquid powder in said lower zone 2.

'7. In a process for contacting two gaseous fluids A and B in separate contact zones I and 2 zone I being above zone 2 with a fluidized powder which is continuously recycled through said zones, the combination of steps comprising passing fluid B through lower zone 2 countercurrent to the flow of powder therethrough at a substantially constant rate sufficient to maintain the powder in said zone in a pseudo liquid state, maintaining a positive superatmospheric pressure of said fluid B above the pseudo liquid powder in said zone, al-

lowing pseudo liquid powder from lower zone 2 to pass unhindered and continuously by the force of gravity and said positive pressure into a transfer zone, said transfer zone communicating with the bottoms of the upper and lower zones I and 2 and bein of restricted cross section compared to said lower zone 2, maintaining a bed of said powder in pseudo liquid state in upper zone I above said lower zone 2, dividing the gaseous fluid A into two portions, passing the first of said portions into the said powder in said transfer zone passing the second of said portions of gaseous fluid A directly into said bed of powder into upper zone I continuously, allowing powder in pseudo liquid state to pass unhindered and continuously by gravity from upper zone I to lower zone 2 and controlling the conditions and circulation rate of said powder by control of the pressure difference between points above the pseudo liquid powder in said two zones and control of the ratio of said two portions of said fluid A, said control of the ratio of said two portions of said fluid A being efiected in response to changes in diiferential pressure between a point above and a point below the level of the pseudo liquid powder in said lower zone 2.

8. In a process for contacting two gaseous fluids A and B in separate contact zones I and 2 zone I being above zone 2 with a fluidized powder which is continuously recycled through said zones, the combination of steps comprising passing fluid B through lower zone 2 countercurrent to the flow of powder therethrough at a substantially constant rate suflicient to maintain the powder in said zone in pseudo liquid state, maintaining a positive superatmospheric pressure of said fluid B above the pseudo liquid powder in said zone, allowing pseudo liquid powder from lower zone 2 to pass unhindered and continuously by the force of gravity and said positive pressure into a transfer zone, said transfer zone communicating with the bottoms of the upper and lower zones I and 2 and being of restricted cross-section compared to said lower zone 2, maintaining a bed of said powder in pseudo liquid state in upper zone I above said lower zone 2, dividing the gaseous fluid A into two portions, passing the first of said portions into the said powder in said transfer zone passing the second of said portions of gaseous fluid A directly into said bed of powder into upper zone I, continuously allowing powder in pseudo liquid state to pass unhindered and continuously by gravity from upper zone I to lower zone 2 and controlling the conditions and circulation rate of said powder by control of the pressure difference between points above the pseudo liquid powder in said two zones and control of the ratio of said two portions of said fluid A, said controls being effected in response to changes in differential pressure between a point above and a point below the level of the pseudo liquid powder in said lower zone 2.

9. In a process for contacting two gaseous fluids A and B in separate contact zones I and 2 zone I being above zone 2 with a fluidized powder which is continuously recycled through said zones, the combination of steps comprisin passing fluid B through lower zone 2 countercurrent to the flow of powder therethrough at a substantially constant rate sufficient to maintain the powder in said zone in a pseudo liquid state, maintaining a positive superatmospheric pressure of said fluid B above the pseudo liquid powder in said zone, allowing pseudo liquid powder from lower zone 2 to pass unhindered and continuously by the force of gravity and said positive pressure into a transfer zone, said transfer zone communicating with the bottoms of the upper and lower zones I and 2 and being of restricted cross section compared to said lower zone 2, maintaining a bed of said powder in pseudo liquid state in upper zone I above said lower zone 2, dividing the gaseous fluid A into two porassume 15 tions, passing thefirst of said portions into the said powder in said transfer zone passing the second of said portions of gaseous fluid A direct- 1 into said bed of powder into upper zone I, continuously allowing powder in pseudo liquid state to pass unhindered and continuously by gravity from upper zone I to lower zone 2 and controlling the conditions and circulation rate of said powder by control of the pressure difierence between points above the pseudo liquid powder in said two zones and control of the ratio of said two portions of said fluid A, said control of the ratio of said two portions of said fluid A, being effected in response to changes in temperature of the circulated pseudo liquid powder in said lower zone 2. I GEORGE E. LIEDHOLM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,414,852 Burnside et al Jan. 28, 1947' 2,419,245 Arveson Apr. 22, 1947' 

1. IN A PROCESS FOR CONTACTING TWO GASEOUS FLUIDS A AND B IN SEPARATE CONTACT ZONES 1 AND 2 ZONE 1 BEING ABOVE ZONE 2 WITH A FLUIDIZED POWDER WHICH IS CONTINUOUSLY RECYCLED THROUGH SAID ZONES, THE COMBINATION OF STEPS COMPRISING PASSING FLUID B THROUGH LOWER ZONE 2 COUNTERCURRENT TO THE FLOW OF POWDER THERETHROUGH AT A SUBSTANTIALLY CONSTANT RATE SUFFICIENT TO MAINTAIN THE POWDER IN SAID ZONE IN A PSEUDO LIQUID STATE, MAINTAINING A POSITIVE SUPERATMOSPHERIC PRESSURE OF SAID FLUID B ABOVE THE PSEUDO LIQUID POWDER IN SAID ZONE, ALLOWING PSEUDO LIQUID POWDER FROM THE LOWER ZONE 2 TO PASS UNHINDERED AND CONTINUOUSLY BY THE FORCE OF GRAVITY AND SAID POSITIVE PRESSURE INTO A TRANSFER ZONE, SAID TRANSFER ZONE COMMUNICATING WITH THE BOTTOMS OF THE UPPER AND LOWER ZONES 1 AND 2 AND BEING OF RESTRICTED CROSS SECTION COMPARED TO SAID LOWER ZONE
 2. MAINTAINING A BED OF SAID POWDER IN 